The invention relates generally to spacecraft coatings and more particularly to a thermal control coating which maintains spacecraft temperature balance under extended exposure to both particulate and solar radiation.
Control of the temperature of a spacecraft operating in space has become a serious problem due to the damaging effects of solar radiation on coatings used to regulate the spacecraft temperature. Since the temperature of a spacecraft in space is a function of solar radiation absorptance of the coatings used on the exterior of the spacecraft, any change in solar radiation absorptance of the coating will change the equilibrium temperature of the spacecraft. Reflecting coatings, such as white paints, have the desired solar radiation absorptance when initially applied to the spacecraft, but after a brief exposure to the space solar-radiation environment, the solar radiation absorptance increases and this increases the spacecraft temperature. To further compound this problem, spacecraft operating within or outside the Van Allen radiation belts are also exposed to particulate radiation in the form of protons, electrons and other charged particles, which substantially darken the white paints and causes a very rapid and substantial increase in the solar radiation absorptance of these paints rendering them useless for maintaining the temperature of a spacecraft within desired operational limits. Further, extended exposure to particulate radiation affects the physical properties of the coating causing it to become brittle and flake-off. It is therefore apparent that the darkening and flaking-off of the coatings caused by exposure to particulate radiation, presents serious obstacles to maintaining the thermal balance of operating spacecraft.
Other spacecraft thermal control coatings have been developed which use metallized reflecting films, but tests have shown that these films, when exposed to particulate radiation, are also subject to the same effects of increasing solar radiation absorptance (darkening) and embrittlement as the reflective paints.
Thus, there has been demonstrated a definite need for a new thermal coating which maintains a thermal balance in a spacecraft even under extended exposure to particulate and solar radiation. Accordingly, it is an object of the present invention to provide a thermal control coating which does not become brittle upon extended exposure to particulate radiation.
Another object of the present invention is to provide a new thermal control coating which does not darken upon extended exposure to solar radiation.
Still another object of the present invention is to provide a new thermal control coating which maintains a thermal balance in a spacecraft upon extended exposure to particulate and solar radiation.